The occurrence of Ewing's sarcoma represents approximately 1% of all cancers reported in children. However, Ewing's sarcoma comprises approximately 30% of all bone tumors in this age group. The incidence of Ewing's sarcoma in the United States for whites less than 20 years of age is 2 cases/million population per year. Ewing's sarcoma rarely occurs in black populations and there is a progressive increase in the incidence during the first two years of life. Presently very little is known about the etiology of Ewing's sarcoma as reflected by the paucity of epidemiologic investigations of this rare occurring tumor. We propose to conduct an analytic epidemiologic study designed primarily to generate etiologic hypotheses for Ewing's sarcoma. In addition, specific hypotheses relating to the frequency of congenital anomalies in individuals and family members, stature and ethnicity will be investigated in this study. Incident cases of Ewing's sarcoma will be ascertained utilizing the resources of the Childrens Cancer Study Group, a national cooperative clinical trials group which includes 29 major pediatric oncology centers. It is estimated that this cooperative group identifies approximately one-third of all cases of pediatric malignancy in the United States. Quantitation of the risk associated with specific factors of exposures will be made by contrasting the cases of Ewing's sarcoma to age, sex, and race-matched regional population controls. Control selection will be made utilizing a modification of random digit dialing and interviews with parents of cases and controls will be conducted by telephone.